import javafx.scene.transform.Scale;

import java.util.Scanner;

public class TestB {
    public static void main(String[] args) {
        double x,y,x1,y1,t;
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()){
            x = sc.nextDouble();
            y = sc.nextDouble();
            x1 = sc.nextDouble();
            y1 = sc.nextDouble();
            t=(x1-x)*(x1-x)+(y1-y)*(y1-y);
            double d = Math.sqrt(t);
            System.out.printf("%.2f",d);
        }
    }
}
